Homemade grinder. Important points.
There are many designs of homemade grinders. Some make them using an engine from an old washing machine, others make them from an old grinder or drill, but all these models share the same technical details. Let's look at them in more detail.
Dimensions and design
There are no specific sizes that are the same for all grinders; they can be purely individual in each specific case. When choosing the overall dimensions and design of a belt grinding machine, you need to be guided by the free space in your workshop and the rule that the longer the belt, the more resistant to abrasion it will be and, accordingly, the less often it will have to be changed. If you are going to purchase ready-made, already glued tapes for the grinder, then the machine needs to be designed taking into account the size of these tapes. If you are going to glue the tapes yourself, then the dimensions of the machine can be arbitrary, but it is best to stick to the standard sizes of the tapes.
Abrasive belts for grinders are available in two widths: 50 and 100 m. The length of such tapes can be 610, 915, 1230, 1600, 1800, 2000 millimeters.
It is best if you have an abrasive belt of the required length, then it will be easier to adjust the size of the grinder to it.
The main components of the grinder are a machine frame with a work table and a tape clamp, an electric motor with a drive roller, a tension roller, a barrel-shaped roller and, if necessary, additional driven rollers. The barrel roller can also be a tension roller.
The most compact grinder can be made with just two rollers, one driven on the electric motor shaft, and the second barrel-shaped tension roller.
If the grinder will work with long abrasive belts, then it will not be possible to do without additional driven rollers.
Why do you need a barrel shaped roller? When assembling the machine, it is almost impossible to maintain perfect parallelism of the axes of all rollers. For this reason, the tape tends to come off the rollers. To eliminate this drawback, a barrel-shaped roller is used. By adjusting the tilt of its axis, you can “force” the abrasive belt to remain in place.
To adjust the axis of the barrel roller, you can use the principle of a regular door hinge. The roller axis is welded to the movable part of the hinge, and adjustment is made using a bolt. Which rests on the movable part of the loop.
The mechanism for tensioning the abrasive belt can be made in several ways. The most common is using a spring, the second is using a furniture gas shock absorber and the third is using regular rubber, for example from a bicycle inner tube. If you use a furniture gas shock absorber, you need to know that it does not work well at low temperatures.
It is recommended to make the tape support two-layer. Make the base of the stop from a metal sheet and glue smooth porcelain tiles onto it. Thus, the emphasis will practically not heat up during intensive work on the grinder. Also, porcelain tiles wear out much slower than metal. It can be conveniently replaced as it wears out; you just need to heat the connection with a hair dryer, and it will come off. You can glue it to a regular silicone sealant for marble, for example Silirub MA from Soudal.
The stop must be adjustable relative to the tape. It must be moved to the tape tangentially to it or with a slight overhang of up to 0.5 mm. This overhang does not cause excessive wear of the belt, but it allows you to grind long strips longitudinally without touching the convex parts of the rollers.
How to calculate the diameter of the drive roller.
To calculate the diameter of the drive roller, you need to know the belt speed at which the grinder will operate and the number of engine revolutions.
Formula for calculating belt speed:
V tape (m/s) = (3.14* D * N) / 60000,
where D is the diameter of the drive wheel in mm, N is the engine revolutions per minute.
Formula for calculating drive roller diameter:
Calculation example. It is necessary to calculate the diameter of the drive roller for processing steel (22-25 m/s). Electric motor 2800 rpm.
The speed of rotation of the belt for different materials can be adjusted by changing the diameter of the drive roller or adjusting the engine speed. It should also be understood that as the diameter of the drive roller increases, the load on the engine increases and if it is of low power, for example, from a washing machine, then it will often stop even from a slight load.
Which engine to choose for a grinder.
Below is the formula for calculating engine power for a grinder.
Formula for calculating engine power:
where D is the diameter of the drive wheel in mm, N is the engine revolutions per minute.
If a three-phase motor is used, but connected to a single-phase 220V network, then its calculated power when connected in a delta with a working capacitor is approximately 1.5...1.6 times lower than the nominal value. This must be taken into account. For example, according to calculations, an electric motor with a power of 800 watts is required, and the motor will be used three-phase, but on a 220V network. Then the required power of such an engine will be equal to: 800 * 1.6 = 1280 watts.
The optimal choice is a single-phase motor with a speed of at least 2800-3000 and a power of at least 800 watts. With such an electric motor, it will be possible to process hardened steel on a grinder, and not just sharpen “pencils.”
If an open-type motor is used in the manufacture of a belt grinding machine, as in washing machines, then you should think about protecting it from abrasive and metal dust. Such protection can be made from a 5-liter plastic bottle or any other plastic container.
How to make rollers for a belt sander
If you know a turner, then you should not have a similar question. Well, if there are no such acquaintances, then this information will be useful to you.
There are several ways to make videos.
It is convenient to make the drive roller from a sheet of plywood. First, circles of the required diameter are marked, then they are cut out using a jigsaw. After this, the plywood circles are glued together.
After gluing, the central hole of the roller is drilled to match the diameter of the electric motor shaft. Now you need to make a keyway in the hole. It is easy to do with a file.
Then we put the roller on the electric motor and grind it using a chisel, a large file or an angle grinder (grinder) with a grinding wheel.
To make the drive roller slip less, it can be treated with liquid rosin.
The easiest way to make driven rollers is to simply assemble them from bearings of a suitable diameter on a shaft. Partially threaded bolts can be used as a shaft. Bearings need to be sealed, otherwise they will quickly become clogged with dust and fail.
You can use timing belt rollers from your car as rollers, but don’t buy new ones, ask them at any service station. It is only desirable that the rollers be flat without shoulders. These beads can cut the edges of the tape.
Another way is to cut the rollers with a crown made from a sheet of plywood and glue the resulting washers together. You can additionally secure them with self-tapping screws. Afterwards, inside the roller you need to drill two holes on both sides of the roller for the bearings. The depth of such holes should be equal to the width of the bearings. It is convenient to drill such holes using a wood drill bit. When the holes are ready, we drill a through hole in the center of the roller for the roller axis. The diameter of this hole should be slightly larger than the diameter of the inner race of the bearing, otherwise the bearing will jam inside the roller.
After this, the roller is almost ready, all that remains is to sand it on the outside and give it the desired shape, if it is a barrel-shaped roller.
The rollers can be made from round caprolon or another name for this material is polyamide-6. The process of making a video is no different from the previous ones. We cut the workpiece to the required length, drill holes with a feather drill for the bearings and grind it on the outside using a grinder.
Engine for grinder, suitable or not
Have a good time everyone. The question is whether the engine will fit. Needed for a grinder, balcony version, belt length 610 and 915 mm, drive pulley diameter 80 and 125 mm, respectively. I liked this engine due to its dimensions and weight, it is small and cultured. But, if you connect to 220V through a triangle, there is a big loss. If you connect through a capacitor, the loss is less, but after 5 minutes the shaft heats up a lot. It makes sense to buy a single-phase 220V 1.1kW motor or it is better to buy a Vladikavkaz frequency generator 220V to 380V. I can’t decide, maybe someone can tell me what.
If possible, of course a frequency generator is better.
Um, here you have an attempt to mix warm with soft. The motor is three-phase; it must be connected directly to a single-phase network in a triangle with a phase-shifting capacitor at the rate of approximately 7 microfarads per 100 watts of power. In this case, its power will be approximately 70% of the nominal value. If you have money, then a frequency generator plus a three-phase circuit is an order of magnitude more interesting than a single-phase circuit of the same power.
sergVs
Um, here you have an attempt to mix warm with soft.
sergVs
If you have money, then a frequency generator plus a three-phase circuit is an order of magnitude more interesting than a single-phase circuit of the same power.
moroz05
Well, I wouldn’t say, we tried raising it from 70 µF to 84 µF.
sergVs
If you turn it without a load, it can still heat up due to the asymmetry of the currents in the windings for the calculated capacitance of the capacitor.
Master Vilya
but when shooting triggers there is not enough power. 1.1 kilo is enough
People, there is a stupid question, but it doesn’t give me any peace). My knowledge of the electrical part is at a rudimentary level, I asked more experienced ones, but also did not receive an intelligible answer. Why can’t you make a simpler system for adjusting speed than a frequency regulator, for example a seven-actor regulator, or is it only suitable for motors with brushes? Somehow the price tag for these frequencies is inhumane.
For asynchronous ones it makes no sense. The rotation speed is strictly determined by the frequency of the supply voltage and the design of the stator. Voltage regulation is only for synchronous synchronizers, and even then without feedback with a drop in power, which is not always acceptable.
